The cell membrane which is the interface between self and non-self carries out many functions essential to life. A large group of membrane antigens which have been identified over the last 25 years were studied for varying intervals without knowledge of their functions. In recent years functions or associations have been demonstrated for several of these antigens, the classical examples being the role of H-2D and H-2K in surveillance, the role of Ia in cell-cell interactions, the differentiation of subclasses of lymphocytes by TL, Thy-l, and Ly antigens and the association of oncogenesis with certain viral cell surface antigens. The functions of most of the membrane antigens remain unknown, but with time and effort those of additional antigens will be discovered. It is to this end that this proposal is addressed -- the elucidation of the distribution, structure and function of a group of membrane antigens under the genetic control of Chromosome-7 genes. This genetic cluster contains at least three H genes as well as four genes involved in the production of viral cell surface structures which have been implicated in oncogenesis. Two of these antigens, H-1 and XenCSA, have not been shown to be distinct. It is the objective of this proposal to study the gene cluster located on Chromosome-7 and the antigens these genes control. Particularly we wish to study the relationship between H-1 and XenCSA, a xenotropic viral cell surface antigen. We will study the distribution, structure, function, and genetic control of the antigens of the Chromosome-7 cluster, as well as the relationship between H-1 and XenCSA.